Aran'gar could enter other people's dreams, which would seem to indicate some natural ability, since Egwene thinks it can't be taught to those who access Tel'aran'rhiod via a ter'angreal. But she sucks at it.

That being said, I do think that Moghedien, Lanfear, and Moridin are the best candidates for Dreamers among the Forsaken. And since one male is confirmed to be a Dreamer, it's really only up in the air as to whether Lanfear or Moghedien is a Dreamer, or both. (And again, I'm talking about prophetic dreams. Just so we don't go around in circles again.)